An accurate evaluation of the exposure of a worker to concentrations of toxic airborne particulate material requires a sampling technique which produces a representative sample of the airborne particulate concentration existing in the air actually breathed by the worker.
Presently, breathing zone sampling is carried out using an open-faced filter assembly that clips to the lapel of a worker. One example of such a sampling arrangement is disclosed in U.S. Pat. No. 4,389,903 (Bertone et al.) wherein a filter unit is clipped to the collar of a miner or other worker and is connected by a conduit to a pump housed in a unit clamped to the belt of the worker. Because the concentration of airborne particulates can vary appreciably over very short distances, i.e., distances as small as several inches, the spacing between such a lapel sampler filter and the actual breathing zone of the worker can lead to results which are not truly representative, i.e., results which do not accurately portray the actual particulate concentrations experienced by the worker. In addition, such lapel sampler filters are typically orientated vertically, so that air flow detected is horizontal which is different from the vertical upward flow into the nose of worker. Further, the velocity of the sampled air entering the filter media rarely, if ever, matches the velocity of the air entering the nose of the worker.